The broad long-term goal of the project is to extend our knowledge of the temporal and spatial properties of the tactile sensory system. Of the four psychophysical channels of the glabrous skin of the hands of humans (P, NP I, NP II, and NP III) only the P channel with its Pacinian corpuscles as receptors and PC peripheral nerve fibers have been found to be capable of temporal and spatial summation. In temporal summation, sensory thresholds decline as a function of the duration of the stimulus, and in spatial summation the threshold declines as the size of the stimulus increases. It is our objective to determine the nature of the underlying processes responsible for summation in the P channel and from this knowledge to attempt to determine why summation is absent in the NP channels. The two processes known to operate in temporal and spatial summation in sensory systems are neural integration in which neural activity increases as a function of either the duration or the size of a stimulus and probability summation in which, because of variability in sensitivity the probability of exceeding the neural threshold increases as either the duration or the size of the stimulus increases. It is our objective to determine the role of these processes in temporal summation and spatial summation in the tactile sensory system. It is also our objective to determine the contributions of each of the four channels to the perception of complex spatio- temporal displays of varied texture, and in so doing to test the hypothesis that the perception of a particular perceptual attribute, such as roughness or clarity, arises from the combined activity of multiple channels rather than from the exclusive activity of a single channel.